OCR Text |
Show 13 been measured at Pueblo and Trinidad, Colo., and Cimarron, Fort Union, Las Vegas, and Santa F6, N. Mex. After the connections shall have been completed at the close of the present field- season, the geographical positions at the vertices of the main and secondary triangles should be computable from the extremity of any of the above bases as initial points, thus giving several results for each position arrived at from original and independent data. The extremities of the bases at the above- mentioned points are joined with the main, astronomical points that have been established in their immediate vicinity. These points have all been carefully marked by euduring monuments, and the extension of the work can be developed from each in all directions at will. Angles of the main triangles have been measured by four of the moving field- parties, and the connections completed over large areas in Colo-rada and New Mexico, with the exception of a few points to be occupied early during the present season. A preliminary sketch, based upon observations made by assistants L. Nell, G. Thompson, F. A. Clark, F. O. Maxson, J. C. Spiller, aud E. J. Sommer, members of parties under command of Lieutenants Marshall, Tillman, Whipple, Price, Birnie, Blunt, Hoxie, and myself, confined to an exhibit of the main or primary triangulation, and showing its extension in the Coloradv section of the work, is here introduced. The secondary triangles, other trigonometric connections, and intermediate astronomical check- stations are not shown, as the data obtained for their determination are not yet all reduced. Lists of geographical positions of the several orders of value will be given in the special publication now being prepared. ( See Appendix K, on publications.) This map, or sketch, is of great value for field and office use, in connection with the filling- in of all essential details within the area already embraced by ^ e main triangulation, and also as an index to future connections westward. I The points occupied and to be occupied in Colorado during the pres- 1 ent field season were selected in pursuance of my project submitted to | and approved by the Chief of Eugineers and the honorable the Secretary I . of War, being a part of the system of triangulation and detailed map- I representation pertaining to certain of the rectangles lying within the | region to be occupied as proposed in an earlier project ( April 3,1873) I for the systematic and connected prosecution of the work, and which I received the sanction of the Chief of Engineers and the Secretary of War after Congress had made appropriation for contiuuiug the survey for the ensuing fiscal year. The geographical positions of the main astronomical stations, together with those of the extremities of the measured and developed bases, and of the vertices of the main triangles, carefully computed, form the mathematical basis, and, in the early stage of the construction of the map, are most essential; while the intermediate points, obtained in the secondary triangulation by connection with three well- established points, by latitude- checks, or from meanders of the roads, trails, streams, & c, serve to locate all necessary points that are selected in such close conjunction as to admit of the sketching of the intermediate mountain-topography, so that as far as practicable from the resultant data conjectural contours of the ground expressing differences of elevation of 250 feet, each referable either to an arbitrary or common plane, can be delineated. In limited areas where the sectionizing of the public lands has been accomplished, usually in mountain- valleys encompassed by the geograph- |